Receiving system



L.lume 42, 1942. '.J. HAANTJEs Erkl. 2,285,030

E RECEIVING SYSTEM Filed May 11, 1940 1&1 J@

j uv BY v i ATTORNEY Patented June 2, 1942 RECEIVING SYSTEM Johan Haantjes, Adelbert van Weel, Maximilaan Julius Otto Strutt, and Aldert vander Ziel, Eindhoven, Netherlands, assignors to Radio Corporation of -America, New York, N. Y.

Application May 11, 1940, Serial No. 334,502 v In the Netherlands June 15, 1939 v 1 claim.

The invention relates to a system for amplifying and, if Vdesired after mixing with a local oscillation, separating two or more oscillations.

Suchsys'tems are utilised, for example, in television receivers which serve for the reception of a picture signal consisting of a carrier wave on which the picture currents are modulated, and a sound signal located in`close proximity thereto and consisting of a carrier wave on which the corresponding sound is modulated. The frequency of the picture carrier wave is, for example, 45-megacycles per second'v whilst the frequency of the sound carrier wave is, for example, 41.5 megacycles per second.

For the purpose of saving receiving tubes these two carrier waves with the corresponding sidebands are usually amplified in la common highfrequency channel and, if desired after being mixed with a local oscillation, separated from one another and separately detected. The separation of the two signals may be effected in this case, for example, by utilizing two tubes which have the input circuit in common and whose anode circuits include oscillatory circuits respectively tuned to both signals.

If, in addition, in these tubes the oscillations to be separated are mixed with a local oscillation, oscillatory circuits tuned respectively to the intermediate frequency signals formed are incorporated in the anode circuits.

The invention permits further economy in tubes whilst with the system according to the invention the additional advantage of greater amplification r of a greater conversion slope is obtained.

According to the invention, the system comprises a tube which has inter alia a control grid, at least one auxiliary cathode `adapted to emit secondary electrons and an anode whilst to the control grid of this tube are supplied, if desired, jointly with a local oscillation, the oscillations to be amplified and separated and the auxiliarycathode circuit or circuits and the anode circuit of this tube have each included impedances which possess respectively a high value for each of the oscillations to be separated or for each of the intermediate-frequency oscillations vcorresponding to the oscillations to be separated.

The impedances included in the auxiliarycathode circuit or circuits and the anode circuit are preferably oscillatory circuits which are tuned respectively to the frequencies to be separated, y

If the oscillations to be separated are mixed beforehand with a local oscillation it is advisivo able Vto supply this local oscillation via a weak coupling to the control grid. I'

When the system is utilized in a television receiver for separating the picture signal and the sound signal, an oscillatory circuit tuned to the oscillation which is' most amplified in the tube, preferably the sound signal, is preferably incorporated in the circuit of the electrode which has the smallest capacity with respect to the control grid.

The invention will be more clearly understood by referring to the accompanying drawing wherein Fig. 1 represents a system according to the invention which may be utilized in a television receiver without frequency transformation for separating the picturefsignal and the sound-signal from one another.

In the system according to Fig. 2, which is also suitable for use in television receivers, frequency transformation is utilized for the separation of the picture signal and the sound signal.

In Fig. l, I'denotes a tube comprising a cathode 2, a control grid 3, a screen grid 4, an auxiliary cathode 5 adapted to emit secondary elec- These oscillations control the electron current v emitted by the cathode 2, which current is accelerated by the screen grid 4, moves to the auxiliary cathode 5 and causes the latter by electron bombardment to emit a number of secondary electrons which is proportional to this current, which electrons travel to the anode 6 with the result that in the auxiliary-cathode circuit I0 as well as in the anode `circuit II there ows an electron current which comprises the oscillations supplied to the control grid 3.

The auxiliary-cathode circuit I0 includes an oscillatory circuit I2 which is tuned to the sound signal and is coupled with an oscillatory circuit I3 to which the sound signal is transferred. The oscillations occurring at the terminals of the oscillatory circuit I3 are rectified and the low- Y frequency component occurring across fa resistance I4 is supplied to the control grid of an amplifying tube I5 whose anode circuit includes a loudspeaker I6. A diode II serving for rectification is preferably provided within the tube I5.

The anode circuit II of the tube I comprises an oscillatory circuit I8 tuned to the picture signal, which circuit is coupled with an oscillatory circuit I 9 which is also tuned to the picture signal,

The voltage set up across the oscillatory circuit I9 is supplied to the control grid of an amplifying tube 2i). The anode circuit of this amplitying tube includes an oscillatory circuit 2| which is also tuned to the picture signal and which has coupled with it the remainder of the picture receiver, which is not shown in the drawing.

A positive Voltage is supplied to the anode 6 through the oscillatory circuit I8. The auxiliary cathode receives, via the oscillatory circuit I2, a positive voltage from a potentiometer formed by resistances 22 and 23. The junction point of these resistances is connected to earth through the intermediary of a condenser 24.

In the system according to Fig. 2, wherein the oscillations toY be separated are mixed beforehand with a local oscillation, similar components are denoted with the same'reference numerals.

The control gridr3 of the tube I has supplied to it not only the oscillations to be separated which originate from the oscillatory circuit 9 butk also, via a condenser 25, an oscillation generated in a local oscillator 26. This oscillator comprises a tube 21 whose anode circuit includes an oscillatory circuit 23 which is coupled with a coil '29 in the grid circuit. Mixing of the oscillations supplied to thecontrol grid 3 takes place within the tube I. The auxiliary-cathode circuit includes an oscillatory circuit 30 which is tuned to the intermediate-frequency sound signal formed and which transfers the oscillations to an' intermediate-frequency circuit 3| which is also tuned to the intermediate-frequency sound signal and supplies the oscillations to a detector and low-frequency amplifier for the sound, which are not shown in the drawing. In the anode circuit of the tube I is incorporated an oscillatory circuit 32 which is tuned to the intermediatefrequency picture signal formed and is coupled with an oscillatory circuit 33. This circuit supplies the intermediate-frequency picture oscillations to the remainder Vof the picture receiver, which is not shown in the drawing.

Since the tube I has a high mutual conductance, for example 14 mA./Volt, the oscillator voltage at the control grid need not exceed 0.5

volt and the condenser 25 may be small, for exl ample a few tenths of a micromicrofarad so that a Weak coupling between the oscillator 25 and the control grid of the tube I may be suiiicient.

If only a narrow band of frequencies is to be amplied, for example the sound carrier wave with its side-bands, a high impedance of the oscillatory circuit tuned thereto may be chosen, so that the amplification becomes very kintense in this case. In this case this oscillatory circuit is preferably incorporated in the circuit of the electrode which possesses the lowest capacity with respect to the control grid 3 of the tube I.

AWhat we claim is: l

A frequency changing circuit for heterodyning and separating two signal-modulated carriers of different frequencies, comprising an-electron discharge tube having at least a main cathode, a control grid, an auxiliary cathode in the form of a solid plate impervious to electrons adapted upon impact of electrons from the main cathode to emit secondary electrons, and an anode, means for simultaneously impressing both carrier frequencies upon the control grid, a local oscillator loosely coupled to the control grid for impressing a heterodyne frequencyA thereon, and a pair of impedances each included respectively in the circuit of the auxiliary cathode and in that oi the anode and each having respectively a high value for one of the intermediate frequencies resulting from the interaction between the heterodyne frequency and each of the signal-modulated carrier frequencies. f

JOHAN HAANTJES.

ADELBERT VAN WEEL.

MAXIMILIAAN JULIUS OTTO STRUT'I'.

ALDERT VAN DER ZIEL.V 

